1. Field of the Invention
The present invention pertains to disk valves, and in particular to such valves mounted in housings so as to have an eccentric pivot axis.
2. Description of the Related Art
Over the years, specialized designs of disk valves have evolved to meet a variety of needs. In one type of such valve, adapted for use as a check valve, a plate-like valve disk is mounted for rotation about an axis which does not pass through the center of the disk, and is therefore referred to as an "eccentric" axis of rotation. The valve disk mates with an annular valve seat disposed within a conduit-like housing having a central axis. One example of this type of valve is described in U.S. Pat. No. 4,003,394. As explained in the background of that patent, the construction of these types of valves is complex, and attempts have been made over the years to simplify the valve construction. However, further simplifications are still being sought today.
Although the valve disk is of relatively simple construction, being formed basically from a flat plate, fabrication of the valve seat (which is formed in the valve housing) requires a fairly complex machining operation, even though the seating surface is conical, i.e., defines part of a cone. The complexities of fabrication arise, in part, because the axis of the cone defining the seating surface is inclined so as to form an acute angle with the central axis of the valve housing. The valve seat is also inclined at an angle to the central axis of the housing and usually is also positioned at a non-normal angle to the cone axis. The valve seat is a relatively thin "slice" or planar section of the conical surface, approximating a thin plane, and as such may be described as having an elliptical configuration since it cuts the cone at a non-normal angle to the cone axis. As mentioned in U.S. Pat. No. 4,003,394, attempts have been made to relax the stringent manufacturing tolerances required for such valves.
The eccentric mounting of the valve disk, typical with these types of valves, usually offsets the pivot axis with respect to the center of gravity of the valve disk in such a way as to create an imbalance in the valve disk mounting. The direction of flow through the valve housing is usually chosen to oppose the direction of valve closing. Return springs mounted on the pivot shaft have heretofore been relied upon to ensure valve closing under static flow conditions. The valve return springs have been specially designed for this purpose, despite the significant imbalance of the valve disk inherent in valves of this type. Such designs compromise other performance features desirable in a valve of the type considered. For example, water hammer presents serious problems in many industrial applications and can cause a significant amount of damage if appropriate steps are not taken. Where water hammer presents a critical problem, ameliorating measures such as employing conventional twin-flapper check valves have been employed, albeit at the sacrifice of certain performance capabilities of the eccentric disk valves.